confused thinking

Is it possible for a side effect of effexor XR 300 mg. to cause confusion in public gatherings? Yesterday I was at a wedding of a daughter of a very good friend. I was a bit nervous as we went into the church. I actually was thinking for a few minutes that we were at our my friend's wedding (which I was in 35 years ago) and started to argue with my husband about what side of the church to sit on. When we sat down I suddenly realized what was happening. It really scared me and concerned by husband. I have been on 300 mg for about 4 weeks.